Blocking

Stuttering often develops into blocking, where the first letter or syllable becomes very difficult to pronounce and is in effect "blocked" from being spoken. When this happens the larynx closes, halting the flow of air. This closure is very similar to the closure of the larynx during the Valsalva maneuver—a maneuver commonly used as pressure equalization technique by scuba divers and airplane passengers to avoid barotrauma. The Valsalva maneuver intentionally exploits the Valsalva mechanism, which is a natural mechanism involving a group of neurologically coordinated muscles in the mouth, larynx, chest, and abdomen. The speech therapy techniques of "gentle onset" or "passive airflow", where the speaker controls his or her airflow to ease into words, aim to avoid abrupt increases in air pressure, and thereby reduce the likelihood of the Valsalva mechanism activating. Constant use of the Valsalva mechanism in speech can create nerve pathways linking speech to the Valsalva mechanism, making it more difficult to reduce blocking.